Understanding the Inorganic‐Rich Feature of Anion‐Derived Solid Electrolyte Interphase

Abstract Anion‐derived solid‐electrolyte interphase (SEI) has received growing attention owing to its appealing properties like fast ion transport and excellent passivation effect. However, a sophisticated understanding of anion‐derived SEI is lacking. To common wisdom, anion‐derived SEI features an inorganic‐rich composition. Herein, it is reveal that the freshly formed anion‐derived SEI consists of a polymer‐rich outer layer and an inorganic inner layer. Then, the organic components dissolve during the discharge process, while the inorganic species with low solubility are retained in the empty SEI husk. The accumulation of empty SEI husks during cycling forms a reacted lithium (Li) layer, which features a much higher content of anion‐derived inorganic species than the newly formed SEI. Therefore, the acknowledged “anion‐derived inorganic‐rich SEI” actually refers to the reacted Li layer instead of the freshly formed SEI. This work provides fruitful insights on the compositional features of anion‐derived SEI.